It is generally known to persons skilled in the art of power plant technology in aircraft that primarily heat-resistant bearing materials such as M50 (80 MoCr V 42-16, 1.3551) or else heat-resistant care-hardened steels such as M50 NiL (13MoCrNi 42-16-14, 1.3555) are used for the bearing rings of highly-loaded rolling bearings, such as for example the main shaft bearing of aircraft power plants, on account of the high operating temperatures. Said materials, after carburization and hardening in the region of the raceway, have a high hardness, and in the non-carburized core region of the bearing ring, have a high level of ductility. The composition of said material, with the exception of the carbon content, is however constant over the entire cross section of the bearing ring. The different demands on the raceways of the bearing rings, such as high rolling strength and wear resistance, and on the core regions of the bearing rings, such as a high level of ductility, can therefore be realized only to a restricted extent.
One possibility for better meeting the high demands on rolling bearings in aircraft power plants is therefore to produce the rolling bearing rings from a fixed composite of two layers of different metallic materials, that is to say to form the region of the raceway for the rolling bearings from a steel with a very high level of hardness and wear resistance, and to form the core region of the rolling bearing ring from a steel with a high level of ductility.
A rolling bearing ring of said type composed of a composite material is known for example from DE 27 45 527 A1. Said rolling bearing ring is composed of a first ring which forms the raceway for the rolling bodies and is composed of a rolling bearing steel which is alloyed with chrome, and of a second ring which forms the core region of the rolling bearing ring and is composed of a corrosion-resistant steel with a low carbon content. In order to be connected to one another, said two rings, which are formed so as to be of the same volume as one another, are plugged into one another concentrically and are deformed radially, by means of profiled rollers, until a chamber which corresponds to the dimensions of the bearing ring is filled, with the simultaneous formation of the raceways for the rolling bodies. The rings subsequently undergo heat treatment and are fixedly connected to one another by means of shrinkage and are finally finished by means of turning of the diameter and grinding.
A disadvantage of said rolling bearing ring composed of a composite material is that the two rings composed of different materials are jointly and simultaneously deformed tangentially, radially and axially by means of rolling and are connected to one another. It is however known from practice that in particular cold-rolling of high-temperature-resistant and wear-resistant materials can be carried out only to a limited extent, since said materials generally have a different capacity for expansion. As a result, a permanent connection of the two rings is problematic, so that a fixed bond between the rings is only obtained in exceptional cases even with the subsequent shrinkage. Likewise, a thickness of the layers of the two materials which varies over the width of the raceway and is adapted to the respective application cannot be realized with the described method of production. Since the rings are not directly materially connected to one another, a bond of said type has proven to be insufficient with regard to its durability in order to meet the high demands on rolling bearings in aircraft power plants. In addition, a plurality of production steps and tools and also a plurality of split tool dies are required to implement the production method for a bearing ring of said type, as a result of which relatively high production costs are generated for a rolling bearing which is formed with bearing rings of said type.
A further possibility for the production of a rolling bearing ring from a composite material is additionally disclosed by DE 29 38 812 A1. In the rolling bearing ring described in this document, the first ring which forms the raceway for the rolling bodies is likewise produced from a rolling bearing steel which is alloyed with chrome and which is produced by means of punching and drawing a corresponding sheet metal strip. The second ring which forms the core region of the rolling bearing ring is composed, in contrast, of a metal powder which, for connecting to the first ring, is filled together with the latter into a die and is compressed under pressure and at temperatures of between 300° C. and 700° C. in a press. The billet which is generated is subsequently sintered in a furnace at temperatures of between 1100° C. and 1200° C. and is cooled in an oxygen-free atmosphere to 950° C. to 1000° C., and finally, the raceway for the rolling bodies is formed in the rolling bearing ring by means of closed die forging or by rolling.
In a rolling bearing ring produced according to said method, although the two rings of the material composite are also cohesively connected to one another by means of the sintering process, it is also the case here, as a result of the use of a punched metal sheet for the raceway region, that the layer thickness of said raceway is largely constant and cannot be varied in a desirable way in terms of its thickness over the width of the raceway. Likewise, it is also the case in this material composite that the final common rolling or forging of the heat-resistant and of the wear-resistant material for the core region and for the raceway region can be implemented only with a very great deal of expenditure in terms of production. In addition, the expenditure for the production of a material composite of said type has proven to be uneconomical in practice, in particular because a separate die for compressing and for sintering the metal powder must be provided for each individual bearing ring, and also as a result of the complex compression and cooling process of the sintered metal.